Block copolymers with high flory-huggins interaction parameters for block copolymer lithography

ABSTRACT

Block copolymers for use in block copolymer lithography, self-assembled films of the block copolymers and methods for polymerizing the block copolymers are provided. The block copolymers are characterized by high Flory-Huggins interaction parameters (χ). The block copolymers can be polymerized from protected hydroxystyrene monomers or from tert-butyl styrene and 2-vinylpyridine monomers.

REFERENCE TO GOVERNMENT RIGHTS

This invention was made with government support under 0832760 awarded bythe National Science Foundation. The government has certain rights inthe invention.

BACKGROUND

Block copolymers (BCPs) are characterized by their ability tospontaneously self-assemble into dense periodic nanostructures havingdomains with small length scales. In the self-assembly process, factorswhich govern the size of the domains are the degree of polymerization(N) and the Flory-Huggins interaction parameter (χ) which is a measureof thermodynamic interactions between the polymer blocks. If χN is belowa critical value, then the BCP will be disordered. Thus, for a given χ,the degree of polymerization can only be decreased a certain amountuntil the BCP no longer self-assembles. However, the resulting domainsize correlates quite closely with N, thereby rendering this approachless useful for generating small domain sizes for nanolithography.

χ_(BCP) can be approximated as the degree of immiscibility between theblocks of the BCP. The most straightforward way to increase χ_(BCP),therefore, is to increase the difference in polarity between the blocks.For a rough approximation of polarity, solubility parameters can beuseful as they have been tabulated for a broad range of homopolymers.

Poly(4-hydroxystyrene) [P(4-HS)] has a high solubility parameter (24.55(J/cm³)^(1/2)) indicating a high degree of polarity and hydrophilicity.Due to the acidic and reactive nature of the phenol group,4-hydroxystyrene (HS) has been protected before polymerization using avariety of groups. 4-acetoxystyrene, for example, has been employed inliving free radical polymerizations and is deprotected by alkalinehydrolysis. (See, Kanagasabapathy, S.; Sudalai, A.; Benicewicz, B. C.,Macromol. Rapid Commun. 2001, 22, 1076-1080 and Barclay, G. G.; Hawker,C. J.; Ito, H.; Orellana, A.; Malenfant, P. R. L.; Sinta, R. F.,Macromolecules 1998, 31, 1024-1031.) However, anionic polymerizationrequires more stringent protection, hence monomers such as4-tert-butoxystyrene and 4-tert-butyldimethylsilyloxystyrene have beenused and deprotected under reflux with strong acid or reaction withfluoride anion. (See, Se, K.; Miyawaki, K.; Hirahara, K.; Takano, A.;Fujimoto, T., J. Polym. Sci., Part A: Polym. Chem 1998, 36, 3021-3034and Ito, H.; Knebelkamp, A.; Lundmark, S. B.; Nguyen, C. V.; Hinsberg,W. D., J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 2415-2427.)Unfortunately, many polymer blocks that might be polymerized with PHS toprovide useful BCPs are degraded by strong acids and attacked byfluoride anions.

SUMMARY

BCPs for use in block copolymer lithography, self-assembled films of theBCPs and methods for polymerizing the BCPs are provided.

One embodiment of a block copolymer comprises a first polymer blockcomprising polymerized hydroxystyrene and a second polymer block, theblock copolymer having a Flory-Huggins interaction parameter of at least0.15.

The block copolymer can be used in a method of transferring a patterninto a substrate via BCP lithography by: depositing the block copolymerover the substrate and subjecting the block copolymer to conditions thatinduce the block copolymer to self-assemble into a plurality of domains;selectively removing some of the domains, such that the self-assembledblock copolymer layer defines a pattern over the substrate; andtransferring the pattern into the substrate to provide a patternedsubstrate.

In another method of transferring a pattern into a substrate via BCPlithography, a block copolymer of poly(t-butylstyrene-b-2-vinylpyridine) (PtBuSt-b-P2VP) is used. This methodcomprises: depositing the PtBuSt-b-P2VP block copolymer over thesubstrate and subjecting the PtBuSt-b-P2VP block copolymer to conditionsthat induce it to self-assemble into a plurality of domains; selectivelyremoving some of the domains, such that the self-assembled PtBuSt-b-P2VPblock copolymer layer defines a pattern over the substrate; andtransferring the pattern into the substrate to provide a patternedsubstrate.

One embodiment of a method of making a block copolymer having apolyhydroxystyrene block via living anionic polymerization comprises:polymerizing acetal group-protected hydroxystyrene monomers via anionicpolymerization, whereby living anions comprising the polymerizedprotected hydroxystyrene monomers are formed; polymerizing a secondmonomer at the chains ends of the living anions via living anionicpolymerization; and deprotecting the acetal group-protectedhydroxystyrene groups, to form the block copolymer comprising a firstpolymer block comprising polymerized hydroxystyrene and a second polymerblock comprising polymerized second monomer, wherein the block copolymerhas a Flory-Huggins interaction parameter of at least 0.15.

Other principal features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structures of BCPs comprising a PHS block and a secondpolymer block. The second polymer block is: (A) polydimethysiloxane(PDMS); (B) poly(tert-butyl styrene) (PtBS or PtBuSt); (C) poly(3,5-dit-butyl substituted styrene); (D) poly(4-trimethylsilylstyrene) (PSSi);(E) poly(4-methyl styrene); (F) poly(methacrylisobutyl polyhedraloligomeric silsesquioxane) (PMAPOSS); (G) poly(isopropyl methacrylate);(H) poly(4-t-butylcyclohexyl methacrylate); (I) poly(4-t-butyl phenylmethacrylate); (J) polyisoprene (polymerized with P(4-HS)); and (K)polyisoprene (polymerized with P(3-HS)).

FIG. 2 shows the structures of acetal group-protected HS monomers thatcan be used to form the PHS blocks in a BCP via anionic polymerization.(A) 4-(2-tetrahydropyranyloxy)styrene (OTHPSt); (B)4-(2-tetrahydrofuranyloxy)styrene (OTHFSt); (C) 4-(1-ethoxyethoxy)styrene (pEES); (D) 4-(2-methoxymethoxy)styrene; and (E)4-((2-methoxyethoxy)methoxy)styrene.

FIG. 3 is an image of a self-assembled film of a cylinder-formingPtBuSt-b-P2VP BCP in accordance with Example 3.

FIG. 4 is an image of a self-assembled film of another cylinder-formingPtBuSt-b-P2VP BCP in accordance with Example 3.

DETAILED DESCRIPTION

BCPs for use in block copolymer lithography, self-assembled films of theBCPs and methods for polymerizing the BCPs are provided. The BCPs arecharacterized by high Flory-Huggins interaction parameters (χ) and canbe polymerized with low overall degrees of polymerization (N). Such BCPare able to self-assemble into domains having very small dimensions and,therefore, are useful in BCP lithography. The BCPs can be polymerizedfrom HS monomers or from tBS and 2-VP monomers.

The BCPs are characterized by χ values of at least 0.15. This includesBCPs having a χ of at least 0.3 and further includes BCPs having a χ ofat least 0.5 and at least 1. For the purposes of this disclosure, χ isdetermined using small angle x-ray scattering (SAXS) and fitting thetemperature dependent correlation hole scattering. The method isdescribed by Seeger et al. in Macromolecules 1990, 23, 890-893. In thismethod, the correlation hole scattering is taken at differenttemperatures above the Tg of the BCP and the data is fit to theequations of state governing a disordered BCP. Plotting the calculated χvalues versus inverse absolute temperature allows the calculation ofχ=α/T+β. For the purposes of this disclosure, the recited χ values referto those values at the highest Tg for the polymer blocks of the BCP.

The BCPs that are polymerized from HS monomers comprise a first polymerblock polymerized from HS monomers and a second polymer block. Thehydroxystyrene can be 4-hydroxystyrene (p-hydroxystyrene) or the meta-or ortho-substituted isomers thereof. The HS monomer may be substitutedor unsubstituted. However, substituents that would increase the polarityof the monomers are typically disfavored since they can have deleteriouseffects on solubility and can increase Tg.

The second polymer block is polymerized from monomers whose homopolymershave a lower solubility parameter that does polyhydroxystyrene. In termsof Hildebrand solubility parameters, this means lower than about 24(J/cm³)^(1/2). This includes monomers having a Hildebrand solubilityparameter of no greater than 20, no greater than 19, no greater than 18and no greater than 16 (J/cm³)^(1/2). The difference between theHildebrand solubility parameters of the two polymer blocks can be, forexample, at least 4 (J/cm³)^(1/2), at least 6 (J/cm³)^(1/2) or at least8 (J/cm³)^(1/2).

Examples of monomers that can be polymerized to provide the second blockinclude polydimethylsiloxane (PDMS). The structure of a BCP comprising afirst polymer block of PHS and a second polymer block of PDMS(PHS-b-PDMS) is shown in FIG. 1A. Other examples include substitutedstyrene monomers, such as tBuSt; 3,5-di t-butyl substituted styrene;(4-trimethylsilylstyrene) (SSi); and 4-methyl styrene. The structures ofa BCP comprising a first block of PHS and a second block of each ofthese monomers are shown in FIGS. 1B, 1C, 1D and 1E, respectively. Stillother examples include methacrylate monomers, such as methacrylisobutylpolyhedral oligomeric silsesquioxane (MAPOSS); isopropyl methacrylate;4-t-butylcyclohexyl methacrylate and 4-t-butyl phenyl methacrylate. Thestructures of a BCP comprising a first block of PHS and a second blockof each of these monomers are shown in FIGS. 1F, 1G, 1H and 1I,respectively. Alternatively, the second block of the BCP can bepolymerized from diene monomers, such as isoprene or butadiene. Thestructures of a BCP comprising a first block of PHS and a second blockof trans-1,4-polyisoprene are shown in FIGS. 1J and 1K, respectively.The second block could also be polymerized from 3,4-polyisoprene.However, in some embodiments, the second polymer block is not a dienepolymer because, as elastomers, they can be difficult to process.

In the BCPs the mass ratio of PHS to the second polymer block willdepend on the degree of polymerization and the desired domain size andmorphology. By way of illustration only, in some embodiments of the BCPsthe mass ratio of PHS to second polymer block is in the range from about20:1 to about 1:1.

The overall degree of polymerization, N, of the BCPs can be controlledexperimentally. N is desirably high enough that the product χN equals orexceeds the critical value for phase segregation for a desired phase(e.g., lamellae, cylinders, spheres, gyroids, etc.) However, N is alsodesirably minimized in order to provide phase domains with smalldimensions.

The PHS-based BCPs can be made using sequential living anionicpolymerization reactions by selecting appropriate protecting groups forthe hydroxy group of the HS monomer. More specifically, acetalprotecting groups that can be removed under relatively mild conditionsare used in order to avoid the degradation of the second polymer blockduring the deprotection process. The acetal protecting groups are formedby reacting the hydroxy group with a moiety that reacts with saidhydroxy group and converts it into an acetal group. The resultinghydroxystyrene derivative is referred to as an acetal group-protectedhydroxystyrene. Some of the acetal protecting groups can be deprotectedunder mildly acidic conditions, such as those provided by a dilutesolution of hydrochloric acid at low temperatures. For example, in someembodiments of the methods, complete deprotection can be carried out ina dilute HCl solution (e.g., having a concentration of ≦20 ppm) at atemperature of 23° C., or lower, over a period of 5 hours or less.

The use of living anionic polymerization to form PHS block-containingBCPs is illustrated in Examples 1 and 2 below. The basic steps of theprocess are as follows: acetal group-protected HS monomers arepolymerized using anionic polymerization to create living anionscomprising the polymerized, protected HS. These living anions are thenchain extended via living anionic polymerization by exposing them to asecond monomer to form a block copolymer comprising a first block ofpolymerized, protected HS and a second block polymerized from the secondmonomers. The acetal groups of the protected HS are then converted backinto hydroxy groups to provide the final deprotected BCP.

The acetal protecting groups can be alkyl acetals characterized by theformula:

—O—(CHR¹)—O—R²

where R¹ is independently hydrogen or a substituted or unsubstitutedhydrocarbon group and R² is a substituted or unsubstituted hydrocarbongroup. Examples of hydrocarbon groups are the lower alkyl groups, thatis—alkyl groups having 1-6 carbons in the alkyl chain. Substitutedhydrocarbon groups include alkoxy groups, such as lower alkoxy groups.Thus, in some embodiments, the acetal protecting groups are alkoxyalkoxygroups, which include alkoxyalkoxyalkoxy groups. In some embodiments, R¹and R² are joined together by a hydrocarbon chain to provide a ringstructure. Such embodiments include those in which the acetal group is atetrahydropyranyl group or a tetrahydrofuranyl group. FIGS. 2A and 2B,respectively show acetal protected hydroxystyrene monomers that areprotected by a 2-tetrahydropyranyl group (i.e.,4-(2-tetrahydropyranyl)oxystyrene) and by a 2-tetrahydrofuranyl group(i.e., 4-(2-tetrahydrofuranyl)oxystyrene). FIGS. 2C and 2D show examplesof acetal protected hydroxystyrene monomers in which R² is an alkylgroup and FIG. 2E shows and example of an acetal protectedhydroxystyrene monomer in which R² is an alkoxy group.

Other embodiments of the BCPs are polymerized from tBuSt monomers and2VP monomers (P(tBuSt-b-2VP)). Like the BCPs polymerized from HSmonomers, the P(tBuSt-b-2VP) BCPs can be polymerized via living anionicpolymerization, as illustrated in Example 3. The P(tBuSt-b-2VP) BCPs arecharacterized by high values of χ at least 0.25 and have moderate Tgvalues, which facilitate processing by thermal annealing.

Once the BCP has been formed, a layer of the BCP can be deposited on asubstrate using a coating technique such as spin-coating. The BCP canthen be subjected to conditions that induce the formation of a patternof domains in the block copolymer film due to phase segregation. Thestep of subjecting the BCP to conditions that induce it to undergodomain formation include subjecting the BCP to a thermal anneal for atime sufficient to allow the block copolymer to self-assemble intodomains or subjecting the block copolymer to a solvent anneal. During asolvent anneal, the BCP film undergoes swelling as it is exposed to asaturated solvent vapor atmosphere, typically at room temperature (23°C.), for a time sufficient to allow the BCP to self-assemble intodomains.

After the self-assembled BCP layer has been formed, it can be convertedinto an etch mask by selectively removing (e.g., etching) one or more ofthe domains from the block copolymer layer to provide a mask pattern.For block copolymers having an insufficient etch contrast between thepolymers of the polymer blocks, the step of selectively removing domainscan include incorporating metal ions into a domain to form a hardtemplate. Such processes can be carried out using metal seeding, asdescribed in Nature Nanotechnology 2007, 2, 500-506 or atomic layerdeposition (ALD), as described in Adv. Mater. 2010, 22, 5129-5133. Suchmethods may be advantageous when the second block does not containsilicon, as is the case with the PtBuSt-b-P2VP BCPs.

The mask pattern can then be transferred to an underlying substrate.This pattern transfer can be carried out by additive or subtractiveprocesses and, once the pattern transfer is complete, the remainingportions of the BCP layer can be removed. For example, the pattern canbe transferred to an underlying substrate by selectively chemicallymodifying regions of the substrate surface that are exposed through themask by chemical functionalization; by selectively removing (e.g.,etching) regions of the substrate that are exposed through the mask; orby selectively coating (e.g., by material growth or deposition) regionsof the substrate that are exposed through the mask.

In some embodiments, the BCP self-assembles into either a plurality ofcylindrical domains in which the cylinders are oriented perpendicular orparallel with respect to the underlying substrate surface, or into aplurality of lamellar domains in which the lamellar planes are orientedperpendicular with respect to the substrate surface, such that theself-assembled block copolymer layer defines either a hole pattern or astriped pattern over the substrate.

Because the domains in the BCP can be formed with nanoscale dimensions(e.g., with dimensions, such as cylinder diameters, sphere diameters orlamellae thicknesses, of 100 nm, ≦20 nm or ≦10 nm) the features of thepattern transferred into the underlying substrate can havecorrespondingly small dimensions (e.g., hole diameters or stripewidths).

EXAMPLES Example 1 Synthesis of BCPs Comprising PHS Blocks via LivingAnionic Polymerization Using OTHPSt Protecting Groups.

Experimental:

Materials. All reagents were purchased from Aldrich Chemical Co. andused as received unless otherwise stated. Polymerizations were performedusing either inert atmosphere (Ar) techniques or high-vacuum break sealglassware (Hadjichristidis et al. J. Polym. Sci. A Polym. Chem. 2000,38, 3211-3234). Tetrahydrofuran (THF) was dried over Na/benzophenoneketyl and freshly distilled before use. Benzene was stirred over H₂SO₄for 1 week then separated and distilled from CaH₂, then Na.4-(2-tetrahydropyranyloxy)styrene (OTHPSt) was prepared according to amodified literature procedure (Hesp et al. J. Appl. Polym. Sci. 1991,42, 877-883). 3-(2-tetrahydropyranyloxy)styrene (3-OTHPSt) was preparedin an analogous manner using 3-hydroxybenzaldehyde. 4-tert-butylstyrene(tBuSt) was distilled first from CaH₂ under vacuum and thendi-n-butylmagnesium and stored in ampoules under vacuum at −20° C.1,1-diphenylethylene (DPE) was distilled over n-butyllithium.3-(3,5,7,9,11,13,15-Heptaisobutylpentacyclo-[9.5.1.^(3,9)1^(5,15)1^(7,13)]octasiloxan-1-yl)propylmethacrylate (MAPOSS) was purchased from Hybrid Plastics andrecrystallized from methanol (MeOH) and dried in a vacuum oven at 60° C.for 24 h then dissolved in THF. Isoprene was distilled from CaH₂ andthen n-BuLi under vacuum and stored in ampoules under vacuum at −20° C.Hexamethyltricyclosiloxane (D₃) was stirred over CaH₂ at 50° C.overnight then distilled under vacuum. D₃ was then added to a solutionof poly(styryl)lithium in benzene and stirred for 2 hours. The D₃ andbenzene solution were distilled together into ampoules under vacuum andstored at −20° C. Lithium chloride (LiCl) was heated at 110° C. for 48hours and stored in a dessicator. Methanol was deoxygenated either undervacuum or by sparging with Ar.

4-(2-tetrahydropyranyloxy)benzaldehyde. To a suspension of4-hydroxybenzaldehyde (61.1 g, 0.5 mol) in 750 mL dichloromethane (DCM)was added 3,4-2H-dihydropyran (58.9 g, 0.7 mol) and pyridiniump-toluenesulfonate (TsOH) (0.67 g, 2.7 mmol). The reaction was stirredunder nitrogen at room temperature and monitored by thin layerchromatography (CHCl₃ eluent) until complete conversion, approximately 1hour. The reaction was quenched with a saturated solution of sodiumcarbonate and allowed to stir for 10 min. The layers were separated andthe organic layer washed with aq. sodium carbonate twice and water once.The organic layer was dried over sodium sulfate and solvent removed byrotary evaporation. The resulting crude oil was used without furtherpurification. Typical yield, 98 g, 95%. ¹H NMR (400 MHz, CDCl₃) δ 9.89(s, 1H), 7.87-7.78 (m, 2H), 7.20-7.12 (m, 2H), 5.54 (t, J=3.1 Hz, 1H),3.85 (ddd, J=11.3, 9.9, 3.1 Hz, 1H), 3.63 (dtd, J=11.4, 4.0, 1.4 Hz,1H), 2.10-1.92 (m, 1H), 1.89 (ddd, J=7.6, 4.9, 3.2 Hz, 2H), 1.81-1.53(m, 3H).

4-(2-tetrahydropyranyloxy)styrene (OTHPSt).4-(2-tetrahydropyranyloxy)benzaldehyde (93 g, 0.45 mol) was dissolved in1200 mL of THF and methyltriphenylphosphonium bromide (MePPh₃Br) (250 g,0.7 mol) was added with vigorous stirring under nitrogen. The flask wascooled via an external ice bath and a solution of potassiumtert-butoxide (KOtBu) (100 g, 0.89 mol) in 300 mL THF was addeddropwise. After the addition was complete, the reaction was stirredovernight at room temperature. The reaction was then filtered overcelite to remove various salts and the filtrate was concentrated toapproximately 500 mL. This suspension was then poured into 1500 mLhexanes with vigorous stirring and the suspension filtered over celite.Concentration, precipitation and filtration steps were repeated oncemore. Solvent was removed by rotary evaporation and the residue wasdistilled under high vacuum (b.p. ˜120° C.) to yield a colorless oil (60g, 65% yield). For anionic polymerization, OTHPSt was distilled furtherfrom CaH₂ and then NaH under high vacuum. The viscous oil was dilutedwith THF (70% OTHPSt v/v) to allow for easier injection into thereactor. ¹H NMR (300 MHz, CDCl₃) δ 7.37-7.31 (m, 2H), 7.04-6.96 (m, 2H),6.65 (dd, J=17.6, 10.8 Hz, 1H), 5.60 (dd, J=17.6, 1.0 Hz, 1H), 5.41 (t,J=3.3 Hz, 1H), 5.12 (dd, J=10.9, 1.0 Hz, 1H), 3.89 (ddd, J=11.3, 9.3,3.2 Hz, 1H), 3.59 (dtd, J=11.4, 4.1, 1.6 Hz, 1H), 2.22-1.46 (m, 6H). ¹³CNMR (75 MHz, CDCl₃) δ 157.07, 136.53, 131.50, 127.51, 116.70, 112.04,96.54, 62.22, 30.57, 25.45, 19.00.

The scheme for the synthesis of OTHPSt is shown in Scheme 1.

Anionic polymerization of OTHPSt. An oven-dried flask equipped with aPTFE stopcock was cooled under argon and 40 mL of THF was added. Theflask was cooled to −78° C. and sec-butyllithium (sec-BuLi) (1.4 M incyclohexane) (caution: sec-butyllithium is a highly reactive, pyrophoricreagent, handle with care) was added dropwise until a yellow colorpersisted. The flask was slowly warmed to room temperature until thesolution became colorless and then chilled to −78° C. A measured amountof sec-butyllithium was added for the desired molecular weight and thedesired volume of OTHPSt/THF solution (70% v/v) was injected into theflask with stirring, yielding an orange/red color from the living anion.After 30 minutes, methanol was added to quench the chain end and the THFsolution was slowly poured into 400 mL of methanol to precipitate theP(OTHPSt) homopolymer. The polymer was recovered by vacuum filtration asa white powder. The resulting powder was dried under vacuum at roomtemperature.

Chain extension with tBuSt. Following the previous procedure to generatethe P(OTHPSt) living anion, an aliquot of 0.1 mL was removed from theflask by syringe and quickly precipitated into methanol for analysis bygel-permeation chromatography. The desired volume of tBuSt was thenrapidly injected into the flask and stirred for 30 minutes beforemethanol was used to terminate the polymerization. The THF solution wasslowly poured into methanol to precipitate the P(OTHPSt-b-tBuSt) blockcopolymer and the resulting white powder was recovered by vacuumfiltration. The powder was dried under vacuum at room temperature.Typical molecular weights ranged from 3.9 kDa to 50 kDa with PDI'sbetween 1.02 and 1.05.

Eight diblock P(OTHPSt-b-tBuSt) copolymers with varying degrees ofpolymerization within the corresponding polymer blocks were synthesizedwith OTHPSt:tBuSt molar ratios ranging from 2:095 to 1:2. In addition,two triblock (ABA or BAB) P(OTHPSt-b-tBuSt) copolymers having varyingdegrees of polymerization within the PtBuSt blocks or the POTHPSt blockswere synthesized. The number average molecular weights for the POTHPStblock and the BCP and the polydispersity indices for the BCPs, as wellas the molar ratios for the polymer blocks, are shown in Tables 1 and 2.

TABLE 1 Mn Mn PDI OTHPSt: Sample (OTHPSt) (BCP) (BCP) tBuSt 1 4200 76001.03 1:0.8 2 9800 20100 1.02 1:1 3 6200 13800 1.02 1:1.05 4 3400 120001.03 1:2 5 5600 16400 1.02 1:1.7 6 8300 29800 1.03 1:1.8 7 1700 39001.04 1:1.7 8 7000 23200 1.02 1:1.9 9 2300 3800 1.05 1:0.85 10 4210054700 1.03 2:0.95 11 3000 5300 1.05 1:0.8

TABLE 2 Sample Mn Mn Mn Block A:Block (ABA) (1^(st) Block) (Diblock)(Triblock) PDI B:Block A P(tBuSt:OTHPSt:tBuSt) 4300 10400 12600 1.031:1.33:0.95 P(OTHPSt:tBuSt:OTHPSt) 3700 7900 12700 1.03 1:0.9:0.85

Chain extension with MAPOSS. Following the previous procedure togenerate the P(OTHPSt) living anion with the addition of LiCl at thebeginning of the polymerization, 5 molar equivalents of DPE was added tothe flask which generated a dark red color. The reaction was stirred for10 minutes and then a 0.1 mL aliquot was taken by syringe and quicklyprecipitated into methanol. A solution of MAPOSS in THF was then addedrapidly to the polymerization and the solution immediately becamecolorless. The polymerization was stirred for 30 minutes and thenquenched by the addition of degassed methanol. The viscous solution wasthen poured slowly into methanol to precipitate the P(OTHPSt-b-MAPOSS)block copolymer and the resulting white powder was recovered by vacuumfiltration. Typical molecular weights ranged from 5.3 kDa to 70 kDa withPDI's between 1.03 and 1.04.

The scheme for the synthesis of P(OTHPSt-b-MAPOSS) is shown in Scheme 2.

Five diblock P(OTHPSt-b-MAPOSS) polymers having varying degrees ofpolymerization within the corresponding polymer blocks were synthesizedwith OTHPSt:MAPOSS molar ratios ranging from 4:1 to 12:1. The numberaverage molecular weights and polydispersity indices for the POTHPStblock and the BCP, as well as the molar ratios for the polymer blocks,are shown in Table 3.

TABLE 3 M_(n) PDI M_(n) Sample OTHPSt OTHPSt M_(n) BCP PDI BCP (NMR)OTHPSt:MAPOSS 1 12900 1.03 16300 1.04 27900  4:1 2 62000 1.04 70000 1.0385000 12:1 3 3300 1.04 5300 1.04 5900  6:1 4 17200 1.03 21200 1.03 2570010:1 5 39000 1.03 44000 1.03 57900 10:1

Chain extension with D₃. Following the previous procedure to generatethe P(OTHPSt) living anion, an aliquot of 0.1 mL was removed from theflask by syringe and quickly precipitated into methanol. A solution ofD₃ in benzene was then added to the polymerization and the orange/redcolor of the OTHPSt anion slowly faded. The reaction was warmed to 25°C. and stirred for two hours to reach approximately 50% conversion. Thepolymerization was terminated with a solution of chlorotrimethylsilaneand pyridine (1:2) in THF. The resulting solution was poured slowly intomethanol to precipitate the P(OTHPSt-b-DMS) block copolymer and theresulting white powder was recovered by vacuum filtration. Typicalmolecular weights ranged from 9.5 kDa to 25 kDa with PDI's of 1.05.

Polymerization of poly(isoprene) with majority 1,4 microarchitecture andchain extension with 3-OTHPSt. Isoprene was polymerized by addingsec-butyllithium to a solution of isoprene in benzene at roomtemperature. The polymerization was stirred overnight and a smallaliquot taken before being frozen in liquid nitrogen. THF was thendistilled into the flask (˜2:1 THF:benzene) and the flask warmed to −78°C. Upon complete thawing of the solvent, 3-OTHPSt was added to thereaction and the color quickly changed from yellow to orange. Thepolymerization was continued for 30 minutes and then quenched by theaddition of methanol. The resulting solution was then poured slowly intomethanol to precipitate the P(I-b-3-OTHPSt) block copolymer and theresulting rubbery solid was collected by filtration. Typical molecularweights ranged from 10 kDa to 20 kDa with PDI's around 1.06 to 1.08.Typically 93% 1,4 addition and 7% 3,4 from ¹H-NMR.

Deprotection of P(OTHPSt-b-tBuSt). 1.0 g of block copolymer wasdissolved in 50 mL THF and then the solution was diluted with 50 mL ofethanol. If the solution became cloudy, THF was added until a clearsolution was obtained once more. At this point, 0.1 mL of aq. HCl wasadded and the solution stirred overnight. After ¹H-NMR spectroscopyconfirmed complete reaction, the solution was poured into water and thepowder collected by filtration.

Deprotection of P(OTHPSt-b-MAPOSS). 1.0 g of block copolymer wasdissolved in 50 mL THF and then the solution was diluted with 50 mL ofethanol, adding THF as necessary to maintain a clear solution. 5 mL aq.HCl was diluted to 50 mL using deionized water. Approximately 0.06 mLwas added to the polymer solution and stirred until ¹H-NMR spectroscopyconfirmed complete deprotection. Extended reaction time or higher acidconcentration led to MAPOSS degradation. After deprotection wascomplete, the solution was poured into water and the powder collected byfiltration.

Deprotection of P(OTHPSt-b-DMS). 1.0 g of block copolymer was dissolvedin 50 mL THF and then the solution was diluted with 50 mL of ethanol(EtOH), adding THF as necessary to maintain a clear solution. 5 mL aq.HCl was diluted to 50 mL using deionized water. Approximately 0.06 mLwas added to the polymer solution and stirred until ¹H-NMR spectroscopyconfirmed complete deprotection. Extended reaction time or higher acidconcentration led to PDMS degradation. After deprotection was complete,the solution was poured into water and the powder collected byfiltration.

The scheme for the synthesis and subsequent deprotection ofP(OTHPSt-b-DMS) is shown in Scheme 3.

Deprotection of P(I-b-3-OTHPSt). 1.0 g of block copolymer was dissolvedin 50 mL THF and then the solution was diluted with 50 mL of ethanol. Ifthe solution became cloudy, THF was added until a clear solution wasobtained once more. At this point, 0.1 mL of aq. HCl was added and thesolution stirred overnight. After ¹H-NMR spectroscopy confirmed completereaction, the solution was poured into water and the powder collected byfiltration.

Characterization. ¹H NMR, ¹³C NMR and ²⁹Si spectra were recorded inCDCl₃, THF-d₈ or acetone-d₆ using a Bruker Avance-400, a VarianMecuryPlus 300 or Bruker Avance-500 spectrometer with the residualsolvent peak as internal reference. Gel-permeation chromatography (GPC)was performed using a Viscotek 2210 system equipped with three Waterscolumns (HR 4, HR 4E, HR 3) and a 1 mL/min flow rate of THF as eluent at30° C. Monodisperse PS standards were used for calibration. Thermalgravimetric analysis was performed on a TA Instruments Q500 using aheating rate of 10° C. per minute under a nitrogen atmosphere.Differential scanning calorimetry was performed on a TA Instruments Q100using a heating and cooling rate of 10° C. per minute for three cycles.Glass transition temperatures were determined from the third cycle.Samples for small angle x-ray scattering (SAXS) were solvent cast by theslow evaporation of THF solutions and then further annealed at varioustemperatures for 12 hours under vacuum. SAXS was performed both at the12-ID-B beamline at the Advanced Photon Source at Argonne NationalLaboratory using a beam energy of 12 keV (1.025 Å) and using a Rigakuinstrument operating at 45 kV with Cu k-alpha radiation (1.54 Å).Temperature-dependent SAXS was performed using a Linkam DSC stage with a5 minute pre-equilibration delay before data collection at a giventemperature.

Results

Table 4 lists the morphology of the post-anneal self-assembledPHS-b-tBuSt BCP films of Table 1, including the domain dimensions. (Forthe lamellae-forming BCP films, the recited dimension corresponds to theheight of the lamellae (pitch). For the cylinder-forming BCP films, therecited dimension corresponds to the periodicity of the hexagonalarray.)

TABLE 4 Sample Morphology L₀ (nm) 1 Lamellar 10.5 2 Lamellar 20.7 3Lamellar 15.7 4 PHS cylinders 15.8 5 PHS cylinders 19.1 6 PHS cylinders25.4 7 Disordered 8 PHS cylinders 19.5 9 Disordered 10 Lamellar 25.1 11Lamellar 8.8

Example 2 Synthesis of BCPs Comprising PHS Blocks via Living AnionicPolymerization Using Other Acetal Protecting Groups.

4-(2-tetrahydrofuranyloxy)benzaldehyde. To a suspension of4-hydroxybenzaldehyde in dichloromethane (DCM) is added2-chlorotetrahydrofuran and triethylamine (Et₃N). The reaction isstirred under nitrogen at room temperature and monitored by thin layerchromatography (CHCl₃ eluent) until complete conversion. Water is addedand the layers are separated and the organic layer washed with watertwice. The organic layer is dried over sodium sulfate and solventremoved by rotary evaporation. The resulting crude oil is used withoutfurther purification.

4-(2-tetrahydrofuranyloxy)styrene (OTHFSt).4-(2-tetrahydrofuranyloxy)benzaldehyde is dissolved in THF andmethyltriphenylphosphonium bromide (MePPh₃Br) is added with vigorousstirring under nitrogen. The flask is cooled via an external ice bathand a solution of potassium tert-butoxide (KOtBu) in THF is addeddropwise. After the addition is complete, the reaction is stirredovernight at room temperature. The reaction is then filtered over celiteto remove various salts and the filtrate is concentrated. Thissuspension is then poured into hexanes with vigorous stirring and thesuspension filtered over celite. Concentration, precipitation andfiltration steps are repeated once more. Solvent is removed by rotaryevaporation and the residue is distilled under high vacuum (b.p. ˜120°C.) to yield a colorless oil. For anionic polymerization, OTHFSt isdistilled further from CaH₂ and then NaH under high vacuum. The viscousoil is diluted with THF to allow for easier injection into the reactor.

The scheme for the synthesis of OTHFSt is shown in Scheme 4.

4-(1-ethoxy ethoxy)styrene (pEES). pEES can be synthesized according tothe procedures described by Endo et al. in J. Polym. Sci., Part A:Polym. Chem. 2011, 49 (21) 4714-4720 and by Frey et al. in ACS Macro.Lett. 2013, 2, 409-413.

4-(2-methoxymethoxy)benzaldehyde. To a suspension of4-hydroxybenzaldehyde in dichloromethane (DCM) is added methoxymethylchloride and N,N-diisopropylethylamine (i-Pr₂NEt). The reaction isstirred under nitrogen at room temperature and monitored by thin layerchromatography (CHCl₃ eluent) until complete conversion. Water is addedand the layers are separated and the organic layer washed with watertwice. The organic layer is dried over sodium sulfate and solventremoved by rotary evaporation. The resulting crude oil is used withoutfurther purification.

4-(2-methoxymethoxy)styrene. 4-(2-methoxymethoxy)benzaldehyde isdissolved in THF and methyltriphenylphosphonium bromide (MePPh₃Br) isadded with vigorous stirring under nitrogen. The flask is cooled via anexternal ice bath and a solution of potassium tert-butoxide (KOtBu) inTHF is added dropwise. After the addition is complete, the reaction isstirred overnight at room temperature. The reaction is then filteredover celite to remove various salts and the filtrate is concentrated.This suspension is then poured into hexanes with vigorous stirring andthe suspension filtered over celite. Concentration, precipitation andfiltration steps are repeated once more. Solvent is removed by rotaryevaporation and the residue is distilled under high vacuum (b.p. ˜120°C.) to yield a colorless oil.

The scheme for the synthesis of 4-(2-methoxymethoxy)styrene is shown inScheme 5.

4-((2-methoxyethoxy)methoxy)benzaldehyde. To a suspension of4-hydroxybenzaldehyde in dichloromethane (DCM) is added2-methoxyethoxymethyl chloride and N,N-diisopropylethylamine (i-Pr₂NEt).The reaction is stirred under nitrogen at room temperature and monitoredby thin layer chromatography (CHCl₃ eluent) until complete conversion.Water is added and the layers are separated and the organic layer washedwith water twice. The organic layer is dried over sodium sulfate andsolvent removed by rotary evaporation. The resulting crude oil is usedwithout further purification.

4-((2-methoxyethoxy)methoxy)styrene.4-((2-methoxyethoxy)methoxy)benzaldehyde is dissolved in THF andmethyltriphenylphosphonium bromide (MePPh₃Br) is added with vigorousstirring under nitrogen. The flask is cooled via an external ice bathand a solution of potassium tert-butoxide (KOtBu) in THF is addeddropwise. After the addition is complete, the reaction is stirredovernight at room temperature. The reaction is then filtered over celiteto remove various salts and the filtrate is concentrated. Thissuspension is then poured into hexanes with vigorous stirring and thesuspension filtered over celite. Concentration, precipitation andfiltration steps are repeated once more. Solvent is removed by rotaryevaporation and the residue is distilled under high vacuum (b.p. ˜120°C.) to yield a colorless oil.

The scheme for the synthesis of 4-((2-methoxyethoxy)methoxy)styrene isshown in Scheme 6.

Anionic polymerization of acetal group-protected styrene monomers(AGP-St). An oven-dried flask equipped with a PTFE stopcock is cooledunder argon and THF is added. The flask is cooled and sec-butyllithium(sec-BuLi) (caution: sec-butyllithium is a highly reactive, pyrophoricreagent, handle with care) is added dropwise until a yellow colorpersists. The flask is slowly warmed to room temperature until thesolution became colorless and then chilled. A measured amount ofsec-butyllithium is added for the desired molecular weight and thedesired volume of AGP-St/THF solution is injected into the flask withstirring, to form the living anion. After 30 minutes, methanol is addedto quench the chain end and the THF solution is slowly poured intomethanol to precipitate the P(AGP-St) homopolymer. The polymer isrecovered by vacuum filtration as a powder. The resulting powder isdried under vacuum at room temperature.

Chain extension of P(AGP-St) with comonomers. BCPs of the P(AGP-St)swith a second monomer (e.g., tBuSt, MAPOSS, DMS) are polymerized usingthe procedures described in Example 1, whereby a solution of the secondmonomer is added rapidly to a solution of the living anionic P(AGP-St)for a time and at a temperature sufficient to allow for chain extensionvia anionic polymerization of the second monomers at the P(AGP-St) chainends. The reaction is then quenched. The BCPs are then precipitated andrecovered.

Deprotection of P(AGP-St-b-Comonomer). BCPs of the P(AGP-St) and thesecond monomer (e.g., tBuSt, MAPOSS, DMS) are deprotected using theprocedures described in Example 1. 1.0 g of the block copolymer isdissolved in 50 mL THF and then the solution is diluted with 50 mL ofethanol, adding THF as necessary to maintain a clear solution. 5 mL aq.HCl is diluted to 50 mL using deionized water. Approximately 0.06 mL isadded to the polymer solution and stirred until ¹H-NMR spectroscopyconfirms complete deprotection. After deprotection is complete, thesolution is poured into water and the powder collected by filtration.

Example 3 Synthesis of P(tBuSt-b-2VP).

Experimental:

Materials. All reagents were purchased from Aldrich Chemical Co. andused as received unless otherwise stated. Polymerizations were performedusing either inert atmosphere (Ar) techniques. Tetrahydrofuran (THF) wasdried over Na/benzophenone ketyl and freshly distilled before use.4-tert-butylstyrene (tBuSt) was distilled first from CaH₂ under vacuumand then di-n-butylmagnesium and stored under argon at −20° C.1,1-diphenylethylene (DPE) was distilled over n-butyllithium. Lithiumchloride (LiCl) was heated at 110° C. for 48 hours and stored in adessicator. Methanol was deoxygenated either under vacuum or by spargingwith Ar. 2-vinylpyridine (2VP) was distilled first from CaH₂ undervacuum and then triethylaluminum and then stored at −20° C.

Polymerization of P(tBuSt-b-2VP). An oven-dried flask equipped with aPTFE stopcock and 30 mg LiCl was cooled under argon and 40 mL of THF wasadded. The flask was cooled to −78° C. and sec-butyllithium (1.4 M incyclohexane) was added dropwise until a yellow color persisted. Theflask was slowly warmed to room temperature until the solution becamecolorless and then chilled to −78° C. A measured amount ofsec-butyllithium was added for the desired molecular weight and thedesired volume of tBuSt was injected into the flask with stirring,yielding an orange/red color from the living anion. After 30 minutes,0.1 mL DPE was added which immediately generated a dark red color in theflask. A 0.1 mL aliquot was taken using a syringe and quickly added tomethanol to quench the anion. After 10 minutes, 2VP was added to theflask (no discernible color change was observed). After 30 minutes,methanol was added to quench the chain end and the THF solution wasremoved by evaporation. The resulting solid was dissolved in ˜70 mL ofacetone and slowly poured into 400 mL of water to precipitate theP(tBuSt-b-2VP) block copolymer. The polymer was recovered by vacuumfiltration as a white powder. The resulting powder was dried undervacuum at room temperature. Typical molecular weights ranged from 7.7kDa to 41 kDa with PDI's around 1.03 to 1.08.

Characterization. ¹H NMR spectra were recorded in CDCl₃, using a BrukerAvance-400 spectrometer with the residual solvent peak as internalreference. Gel-permeation chromatography (GPC) was performed using aViscotek 2210 system equipped with three Waters columns (HR 4, HR 4E, HR3) and a 1 mL/min flow rate of THF as eluent at 30° C. Monodisperse PSstandards were used for calibration. Thermal gravimetric analysis wasperformed on a TA Instruments Q500 using a heating rate of 10° C. perminute under a nitrogen atmosphere. Differential scanning calorimetrywas performed on a TA Instruments Q100 using a heating and cooling rateof 10° C. per minute for three cycles. Glass transition temperatureswere determined from the third cycle. Samples for small angle x-rayscattering (SAXS) were solvent cast by the slow evaporation of THFsolutions and then further annealed at various temperatures for 12 hoursunder vacuum. SAXS was performed using a Rigaku instrument operating at45 kV with Cu k-alpha radiation (1.54 Å). Temperature-dependent SAXS wasperformed using a Linkam DSC stage with a 5 minute pre-equilibrationdelay before data collection at a given temperature.

Results:

Nine diblock P(tBuSt-b-2VP) polymers were synthesized with volumefractions of P2VP ranging from 0.19 to 0.69. The number averagemolecular weights for the PtBuSt block and the BCP, the polydispersityindices for the BCP and the T_(g) for the BCPs, are shown in Table 4.Also shown in Table 5 is the morphology of the post-annealself-assembled BCP films, including the domain dimensions. (For thelamellae-forming BCP films, the recited dimension corresponds to theheight of the lamellae (pitch). For the cylinder-forming BCP films, therecited dimension corresponds to the periodicity of the hexagonalarray.)

TABLE 5 Sample M_(n) PtBSt M_(n) BCP PDI BCP f_(P2VP) T_(g) (° C.) L₀(nm) (morphology) 1 6.0 10.9 1.03 0.53  99, 134 17.5 (lamellae) 2 6.17.7 1.04 0.23  98, 128 14.2 (P2VP cylinders) 3 7.3 18.9 1.04 0.65 100,138 26.9 (lamellae) 4 17.4 40.6 1.08 0.69 102, 147 50.2 (lamellae) 5 5.311.5 1.04 0.56  98, 128 18.1 (lamellae) 6 5.3 10.0 1.04 0.44  98, 13417.6 (lamellae) 7 7.7 11.4 1.04 0.31 101, 136 20.2 (P2VP cylinders) 88.4 16 1.05 0.48 100, 142 23.2 (lamellae) 9 11.9 14.9 1.04 0.19 100, 13923.0 (P2VP cylinders)

The domain spacing (d) of a lamellar diblock copolymer in the strongsegregation regime (J. Polym. Sci. Part B: Polym. Phys. 2005, 43,3685-3694) is related to the statistical segment length (b), degree ofpolymerization (N) and χ parameter by the following equation

d=1.098*b*N ^(2/3)*χ^(1/6)

By using the known values for b, d, and N (here the volume degree ofpolymerization), rearranging the equation allows for an approximation ofχ for the system. This was done for all lamellar forming BCPs and theaverage χ determined was 0.3. By further extending this concept to thedomain size at different temperatures, the temperature dependence of χcan be estimated. In this case, χ=142.95/T−0.088 where T is in Kelvin,which yields a χ of 0.25 at 150° C. (approx. 10° C. above the T_(g) forPtBS).

FIGS. 3 and 4 show images of self-assembled films of samples 2 and 9from Table 5. In both films the P2VP domains formed cylinders orientedparallel to the substrate. The structures were revealed by seeding theP2VP domain with platinum, followed by a selective etch. The cylinderdiameter for sample 2 was 6.1±0.7 nm. The cylinder diameter for sample 9was 11.4±1.3 nm.

The word “illustrative” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“illustrative” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Further, for the purposes ofthis disclosure and unless otherwise specified, “a” or “an” means “oneor more”. Still further, the use of “and” or “or” is intended to include“and/or” unless specifically indicated otherwise.

The foregoing description of illustrative embodiments of the inventionhas been presented for purposes of illustration and of description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed, and modifications and variations are possible inlight of the above teachings or may be acquired from practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and as practical applications of theinvention to enable one skilled in the art to utilize the invention invarious embodiments and with various modifications as suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A block copolymer comprising a first polymerblock comprising polymerized hydroxystyrene and a second polymer block,the block copolymer having a Flory-Huggins interaction parameter of atleast 0.15.
 2. The block copolymer of claim 1, having a Flory-Hugginsinteraction parameter of at least
 1. 3. The block copolymer of claim 1,wherein the polymer of the second polymer block has a Hildebrandsolubility parameter of no greater than (19 J/cm³)^(1/2)).
 4. The blockcopolymer of claim 1, wherein the second polymer block ispolydimethylsiloxane.
 5. The block copolymer of claim 1, wherein thesecond polymer block comprises a substituted polystyrene.
 6. The blockcopolymer of claim 5, wherein the substituted polystyrene ispoly(4-tert-butylstyrene).
 7. The block copolymer of claim 5, whereinthe substituted polystyrene is selected from poly(3,5-di t-butylsubstituted styrene), poly(4-trimethylsilylstyrene and poly(4-methylstyrene).
 8. The block copolymer of claim 1, wherein the hydroxystyreneis 3-hydroxystyrene and the second polymer block is polyisoprene.
 9. Theblock copolymer of claim 1, wherein the polymer of the second polymerblock comprises a methacrylate polymer.
 10. The block copolymer of claim9, wherein the methacrylate polymer is poly(methacrylisobutyl polyhedraloligomeric silsesquioxane).
 11. The block copolymer of claim 9, whereinthe methacrylate polymer is poly(isopropyl methacrylate).
 12. The blockcopolymer of claim 9, wherein the methacrylate polymer ispoly(4-t-butylcyclohexyl methacrylate) or poly(4-t-butyl phenylmethacrylate).
 13. A polymer film comprising the block copolymer ofclaim 1 self-assembled into a plurality of domains, wherein the domainshave at least one spatial dimension that is no greater than 20 nm.
 14. Amethod of transferring a pattern into a substrate using the blockcopolymer of claim 1, the method comprising: depositing a blockcopolymer over the substrate and subjecting the block copolymer toconditions that induce the block copolymer to self-assemble into aplurality of domains; selectively removing some of the domains, suchthat the self-assembled block copolymer layer defines a pattern over thesubstrate; and transferring the pattern into the substrate to provide apatterned substrate.
 15. A method of making a block copolymer via livinganionic polymerization, the method comprising: polymerizing acetalgroup-protected hydroxystyrene monomers via anionic polymerization,whereby living anions comprising the polymerized protectedhydroxystyrene monomers are formed; polymerizing a second monomer at thechains ends of the living anions via living anionic polymerization; anddeprotecting the acetal group-protected hydroxystyrene groups, to formthe block copolymer comprising a first polymer block comprisingpolymerized hydroxystyrene and a second polymer block comprisingpolymerized second monomer, wherein the block copolymer has aFlory-Huggins interaction parameter of at least 0.15.
 16. The method ofclaim 15, wherein the acetal group has the formula:—O—(CHR¹)—O—R² where R¹ and R² are independently hydrogen or asubstituted or unsubstituted hydrocarbon group.
 17. The method of claim16, wherein R¹ and R² are joined together by a hydrocarbon chain toprovide a 5- or 6-member heterocyclic ring structure.
 18. The method ofclaim 16, wherein the acetal group is an alkoxyalkoxy group.
 19. Amethod of transferring a pattern into a substrate using a PtBuSt-b-P2VPblock copolymer, the method comprising: depositing the PtBuSt-b-P2VPblock copolymer over the substrate and subjecting the PtBuSt-b-P2VPblock copolymer to conditions that induce it to self-assemble into aplurality of domains; selectively removing some of the domains, suchthat the self-assembled PtBuSt-b-P2VP block copolymer layer defines apattern over the substrate; and transferring the pattern into thesubstrate to provide a patterned substrate.